[code-reflection] Integrated: Post dominator functionality

[Paul Sandoz]

On Fri, 30 May 2025 23:04:13 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

> Add functionality to compute immediate post dominators and the post dominator frontier. Also include facilities to obtain a block's predecessor references and successor targets.

Need some of these features for updates to #431, so integrating now. (Can follow up later on better tests for dominance and post dominance.)

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PR Comment: https://git.openjdk.org/babylon/pull/437#issuecomment-2936499158